After upgrading to Telerik UI for ASP.NET AJAX 2026 Q1 (2026.1.211.462) the HtmlChart Sparkline cannot initialize.

The demo page loads, but the chart is empty and the component is not usable.

The browser console shows a JavaScript initialization failure originating from the Telerik scripts.

The first error thrown is:

Uncaught ReferenceError: kendo is not defined
    at Telerik.Web.UI.WebResource.axd...

Immediately after that a second error appears:

Uncaught TypeError: kendo.jQuery(...).kendoSparkline is not a function

The second error is a cascade failure because the Kendo widgets are never registered due to the first error.

 

Hello Telerik Team,

I'm implementing HeaderContext filtering with checkbox lists on a RadGrid in a legacy ASP.NET WebForms application. 

Current Setup:
- FilterType="HeaderContext"
- FilterCheckListEnableLoadOnDemand="true"
- OnFilterCheckListItemsRequested event populates checkboxes from session data

Issue:
Users experience 500-2000ms delay when opening filter menus (AJAX callback to server). 
In our production environment with slow network and high concurrent users, this creates 
poor user experience.

Questions:
1. Is there a way to pre-populate checkbox lists during grid initialization 
   (avoiding AJAX callback)?
2. Can we use OnItemCreated to populate checkbox lists with 
   FilterCheckListEnableLoadOnDemand="false"? If so, what's the correct approach?
3. Is there a client-side caching mechanism for checkbox list items?
4. What's the recommended pattern for large datasets (1000+ rows) with multiple 
   filterable columns?

Environment:
- Telerik.Web.UI version: v4.0.30319
- .NET Framework: 4.8
- Browser: Chrome, IE11
- Grid has ~10 columns with 5 using checkbox filters

Any guidance on performance optimization would be greatly appreciated!

Thank you,
Anurag pandey

When ToolProviderID is set on a consumer RadEditor and tools are added programmatically (via Editor.Tools.Add()), the editor renders duplicate toolbars — one server-rendered from the Tools collection and one loaded client-side from the provider editor via JavaScript.

The issue can be observed in the following demo: https://demos.telerik.com/aspnet-ajax/htmlchart/examples/databinding/clientdatasource/defaultcs.aspx 

The gantt throws Uncaught ReferenceError: kendo is not defined when clicking on the calendar picker button.

The spreadsheet throws Uncaught ReferenceError: kendo is not defined when you type in a number in the quantity field, then click to the next cell.

 

I've updated the Telerik library to 2026 Q1 (2026.1.211.462) and noticed a JavaScript error "ReferenceError: kendo is not defined." is thrown on the page where the RadSpreadsheet is located.

is it possible for the radnumerictextbox control to pop up with numeric keyboards on mobile devices yet?  I see old KB articles that said no, but they were pretty old.

Affected Versions

• Broken: 2025.4.1321
  
• Working: 2025.4.1210 and earlier

Components

RadTabStrip
RadMultiPage
RadPageView

Description
When using RadMultiPage with ScrollBars="Auto" (or any ScrollBars setting), scrollbars only appear on the initially selected tab. After switching to another tab client-side, the scrollbar does not appear even when the content overflows.

The input box for RadOTPInput style are vertical lines instead of text boxes. Your demo site also has that problem, https://demos.telerik.com/aspnet-ajax/otpinput/overview/defaultcs.aspx. Should I downgrade until this is fixed? Currently on 2025.4.1321.462

 

Thanks,

Khanh

Please implement WAI-ARIA support in RadSearchBox with and without a Search Context.

It needs the same type of logic added as the AutoComplete and ComboBox control so that JAWS can speak and navigate the list items properly.
It looks like there was a little started because it renders an ARIA live region for status, but never writes to it from what I can tell.

I know this document lists the current controls that support ARIA - http://docs.telerik.com/devtools/aspnet-ajax/controls/wai-aria-support-and-screen-readers

Thanks,
Mike

When a RadWindow is configured with ShowContentDuringLoad="false" and RenderMode="Lightweight", clicking on dropdown controls (RadComboBox, RadDatePicker, RadDropDownList) at the bottom of the content page causes the scroll position to jump to the top.

After updating to the new version, our RadListBoxes are behaving strangely. This problem is especially apparent when using a RadListBox with checkboxes that need to scroll.

When the RadListBox has enough elements and a restricted height, it lets you scroll through the items. If you check an item's checkbox, the list box appears to select the first item you can see. At that point, the item that appeared selected becomes marked or something, and you will not be able to check or select any other item in the RadListBox unless that item is visible. It also snaps the scroll position of the RadListBox back to the marked row.

We have an old local install of our project running the 2025.3.825 version, and the RadListBoxs work just fine. This issue was likely caused by a change somewhere between the 2025.3.825 and 2025.4.1321 versions.

Steps to recreate:

1. Check an item's checkbox

2. Scroll the items until you cannot see the one you checked.

3. Try to check another item's checkbox.

The InsertLink light dialog has a typo in the for attribute of the URL label, causing a case mismatch with the input's id. This results in accessibility tools like Wave and SortSite reporting the URL textbox as an unlabeled control.
Steps to Reproduce
1. Add a RadEditor with EnableAriaSupport="true" to a page
2. Ensure the InsertLink tool is enabled (it is by default)
3. Click the InsertLink toolbar button to open the dialog
4. Run an accessibility audit using Wave, SortSite, or inspect the DOM

Expected Behavior
The label's for attribute should match the input's id attribute exactly, allowing accessibility tools to correctly associate the label with the input.

Actual Behavior
• Label has for="LinkURL" (uppercase "URL")
• Input has id="LinkUrl" (mixed case "Url")
Since HTML for/id matching is case-sensitive, the label is not properly associated with the input control.

Affected File
InsertLink.ascx

## Description
When RadEditor switches to HTML mode, a `<textarea>` with class `reTextArea` is dynamically created. This textarea lacks proper accessibility attributes, causing WCAG accessibility tools (e.g., Wave) to flag it as an unlabeled form control.

## Steps to Reproduce
1. Create a RadEditor with `EnableAriaSupport="true"`
2. Switch to HTML mode
3. Run Wave or similar accessibility checker
4. Observe the textarea is flagged as "missing form label"

## Expected Behavior
When `EnableAriaSupport` is enabled, the HTML mode textarea should have:
- `aria-label` attribute to identify its purpose
- `aria-hidden="true"` when in Design mode (hidden state)

## Fix
Added ARIA attributes in `_getHtmlModeTextarea()` and toggle `aria-hidden` in `_showTextArea()` based on `EnableAriaSupport` setting.

AutoSize shows a scroll in Chrome. 

See your own Window auto-size demo page

Here is a screenshot from your demo.  See scroll-bars...you must slightly resize bottom right to make them disappear.

https://demos.telerik.com/aspnet-ajax/editor/examples/rendermodes/defaultcs.aspx?skin=Bootstrap

The sizes of the Document Manager & Generate ID buttons in the Hyperlink Manager dialog in Lightweight don't look correct - maybe they should be the same height as the textbox?

Problem
When using RadEditor with Track Changes and Comments features enabled and a non-English language setting (e.g., Language="pt-BR"), the confirmation and result dialog titles for bulk operations display mixed language content.

Affected dialogs:

• Remove All Changes
• Remove All Comments
• Accept All Changes
• Reject All Changes

Example of incorrect behavior:

• Expected title: "Remover Todas as Alterações" (Portuguese)
  
• Actual title: "Remover Comentário All Changes" (mixed Portuguese + English)

Steps to Reproduce

1. Configure RadEditor with EnableTrackChanges="true" and EnableComments="true"
2. Set Language="pt-BR" (or any non-English language)
3. Add some track changes or comments to the content
4. Click on "Remove All Comments" or use any bulk track changes operation
5. Confirm the action by clicking OK
6. Observe the dialog title in the result alert
   
   

Hi
Please add rtl support to RadDropDownTree.

Thanks